A tremendous amount of work has been devoted over the years to procedures for beneficiating coal, i.e. reducing the ash and/or sulfur content of the coal. One of the processes for beneficiating coal has involved grinding the coal to a relatively fine powder and washing the powder with water to separate physically the ash from the coal. This process resulted in a beneficiated coal product having a high water content. Two basic disadvantages resulted. First, a substantial amount of energy was required in heating the coal to evaporate entrapped water. Also, to use the coal in a burner, the coal particles were generally suspended in a liquid fuel. Since the coal particles tended to settle in the fuel, the fuel and coal mixture had to be agitated at least directly before being introduced into a burner. There was no efficient manner for reducing the settleability of the fine coal particles in the liquid fuel for transportation purposes and/or for the actual burning operation. Indeed, the suspended coal often caused abrasive erosion of the burner using the combined coal and liquid fuel mixture. Consequently, a substantial amount of work has also been devoted to processes and procedures for suspending coal in fuel oil, such as the use of emulsifiers as described in U.S. Pat. No. 4,101,293.
The state of the art for providing a mixture of coal particles in a fuel oil mixture has involved pulverizing coal in a manner which entraps substantial water. Thermally extracting the water from the coal was required. The coal was generally mixed with a fuel oil for the purpose of providing a combined oil and coal mixture for use in burners. This combined lower cost coal with the ever increasingly more expensive fuel oil. Since it is advantageous to use a high percentage of coal, suspension of the coal is a primary problem. To assist in the suspension process, emulsifiers have been suggested. Combining these technologies still involves substantial process steps which include thermal extraction of water from the wetted coal particles.
As a separate development, it has been suggested that the pulverized coal can be subjected to a fuel oil and water mixture for cleaning ash from the coal and extracting coal with the oil phase from the mixture. This separated coal is still settleable in the oil. Consequently, there has been no process for beneficiating coal to produce a coal product which is not settleable and does not require intermediate thermal extraction of unwanted volumes of water. Such thermal extraction is a cost addition hindering the use of beneficiated coal.
In a wholly different art there has developed a technology known as chemical grafting. In this process, an organic material can be grafted onto a substrate by the use of site initiators which create locations onto which the organic material can be chemically bonded to the substrate. Although this art is disclosed in certain patents, it has not been used in beneficiating coal. In U.S. Pat. No. 4,033,852 (Horowitz) chemical grafting is disclosed as a means for making a percentage of coal soluble in a solvent. This soluble coal in a solvent does not incorporate suspended coal particles and can not be used in high volume production of a burnable fuel since the amount of coal actually made soluble by the chemical grafting process is relatively small compared to the bulk of coal being used. This patent is mentioned in that it employs chemical grafting with a coal product; however, it is not being disclosed for the purpose of teaching the use of chemical grafting in a coal beneficiating process.
Chemical grafting, as disclosed in the Horowitz patent, is made to occur in the presence of minor amounts of additive chemicals which include a polymerizable unsaturated vinyl monomer constituting from 0.5 to 10% by weight of the coal to be treated and a free radical catalyst system in the range of from 0.001 to 0.010 wt. percent of the monomer. The free radical catalyst system consisted of an organic peroxide catalyst added to the reaction in an amount between 0.01 to 2.5 wt. percent of the monomer. A quantity of free radical initiator metal ions are present in said free radical catalyst system, usually noble metals. Monomers said to be useful for chemical grafting to the coal included vinyl oleate, vinyl laurate, vinyl stearate and other well established and well known monomeric, unsaturated natural or synthetic organic compounds.
The metal ion catalyst initiator disclosed in the Horowitz patent was silver originating from silver salts including silver nitrate, silver perchlorate and silver acetate. U.S. Pat. No. 3,376,168 (Horowitz) discloses that other metal ions, such as platinum, gold, nickel or copper can be used when chemically grafting the foregoing polymerizable monomers onto the backbone of preformed polymers, illustratively, cellophane and dinitrated nitrocellulose. This patent does not relate to increasing the solubility of coal.
As further background, for many years it has been known that finely divided coal particles could be agitated under specific control conditions with carefully selected liquid hydrocarbon fuels to cause preferential wetting of the coal surface with the water insoluble fuel fraction in an aqueous admixture. The process is known under the identification "Spherical Agglomeration." Summary reports in spherical agglomeration process development apparently show that the specific gravity of the hydrocarbon liquid, its origin and chemical and physical quality and the nature of the agitation are all inter-related. Operational variables appear to be critical and present substantial impediments to uniform operation. The coal particles used in this process are previously crushed to a fine powder, i.e. less than about 200 mesh, and often thermally dried. Also, the resulting product exhibits a common deficiency of short shelf life and difficulty in use with a burner.
As further background, it has been generally known as to equipment and methods for reducing mined coal to various particle sizes by crushing, grinding and pulverizing coal in either a dry state or when wetted by water. For background in such processes, Coal Age for January 1978, pages 66 through 83 has a portfolio of flow sheets of presently used processes.
As a summary of background for the present invention, it is apparent that efforts have been made to render coal more acceptable and economic as a source of energy. Systems have been suggested for beneficiating coal by crushing the coal into small sized particles and washing these particles for removal of ash and residue. Systems have been developed for mixing coal particles with fuel oil for use in burners, thereby taking advantage of the low cost and availability of coal. Each of these systems has disadvantages which have prevented its widespread use.